1. Field of the Invention
The present invention relates to a piezoelectric/electrostrictive device having a light modulation mechanism for use in an image display unit, an image printing unit, an exposure unit, an optical switch, or a like apparatus.
2. Description of the Related Art
Recently, various devices having light modulation mechanisms have been developed. For example, Japanese Patent Application Laid-Open (kokai) No. 5-196880 discloses a deformable mirror device (hereinafter called a DMD). As shown in the schematic perspective view of FIG. 33, the DMD includes a CMOS substrate 200; two support elements 202 disposed on the substrate 200; a pair of torsion hinges 204 supported by the support elements 202; a yoke 206 supported by the support elements 202 via the torsion hinges 204; and a mirror 208 supported by the yoke 206. The torsion hinges 204 are twisted through utilization of electrostatic attraction, to thereby change the angle of the mirror 208. For easy understanding, the mirror 208 in FIG. 33 is represented as being transparent.
The DMD is said to enable reduction in device size and highly dense arrangement of pixels. However, since the torsion hinges 204 are twisted so as to drive the mirror 208, the torsion hinges 204 tend to suffer fatigue. Also, since electrostatic attraction is utilized for driving the mirror 208, the mirror 208 may be stuck during operation.
As shown in the schematic sectional view of FIG. 34, a thin-film actuated mirror array (hereinafter called AMA) disclosed in Japanese Patent Application Laid-Open (kokai) No. 11-72724 includes an actuating portion 312 supported by an anchor 302 formed on a substrate 300. The actuating portion 312 consists of a support layer 304 supported by the anchor 302, a bottom electrode 306 formed on the support layer 304, a deformable layer 308 containing a piezoelectric substance and formed on the bottom electrode 306, and a top electrode 310 formed on the deformable layer 308. A stress balance layer 316 is supported on the actuating portion 312 via the post 314, and a light-reflecting member 318 is formed on the stress balance layer 316. Voltage is applied between the bottom electrode 306 and the top electrode 310 so as to deform the deformable layer 308. Through deformation of the deformable layer 308, the actuating portion 312 is inclined, to thereby incline the light-reflecting member 318. For changing the angle of the light-reflecting member 318 the AMA utilizes deformation of the deformable layer 308 containing a piezoelectric material instead of torsional movement of a torsion hinge. As a result, a drive part is less likely to suffer fatigue. Also, since the AMA does not employ electrostatic attraction, the light-reflecting member 318 is unlikely to become stuck.
However, the AMA involves the following drawbacks. Since the light-reflecting member 318 is formed in parallel with the deformable layer 308, the length of the deformable layer 308 must be increased when a large deflection angle (the angle of tilt of reflective surface) is required. As a result, the size of the element increases. Also, since the light-reflecting member 318 is formed of a thin metal film, whose rigidity is low, the reflective surface implemented by the light-reflecting member 318 encounters difficulty in maintaining flatness. Since the flatness of the reflective surface changes with time as a result of operation of the AMA, the operation of deflecting the reflective surface cannot be performed stably over a long period of time.
An object of the present invention is to solve the above problems involved in the DMD and the AMA and to provide a piezoelectric/electrostrictive device enabling an increase of deflection angle without involvement of an increase in the size of an element and which is less susceptible to time-course deterioration in a drive part, as well as to provide a method for fabricating the device.
To achieve the above object, the present invention provides a piezoelectric/electrostrictive device comprising a functional element, which, in turn, comprises a base portion; a deformable portion assuming the form of a thin plate and extending from the base portion to thereby form a plane; a piezoelectric/electrostrictive element tightly fixed to at least the deformable portion; and a reflective portion extending from the deformable portion so as to form an active plane intersecting with the plane of the deformable portion, and having a light-reflecting member disposed on the active plane. Upon operation of the piezoelectric/electrostrictive element, the deformable portion deforms in a direction substantially perpendicular to the plane of the deformable portion to thereby change a reflection angle of light reflected from the reflective portion.
In order to change the reflection angle of light reflected from the light-reflecting member disposed on the reflective portion, the piezoelectric/electrostrictive element causes the thin deformable portion to be deformed in a direction substantially perpendicular to the plane of the deformable portion. Thus, no torsion is exerted on the deformable portion, which serves as a drive portion. Therefore, the deformable portion is unlikely to deteriorate with time. Also, since the active plane of the reflective portion on which the light-reflecting member is disposed is arranged in such a manner as to intersect with the plane of the deformable portion, even when the length of the deformable portion is increased in order to increase the deflection angle (the angle of tilt of reflective surface), there is no need to increase the length of the light-reflecting member in association with the increase in the length of the deformable portion. Accordingly, the above-described configuration enables provision of a piezoelectric/electrostrictive device of small size and high reliability, thereby enabling highly dense arrangement of pixels in application to, for example, an image display unit. Notably, the degree of reduction in the size of the piezoelectric/electrostrictive device becomes greatest when the active plane of the reflective portion and the plane of the deformable portion intersect at right angles.
In the above piezoelectric/electrostrictive device, the reflective portion preferably extends from an end part of the deformable portion while having a width substantially equal to that of the deformable portion.
Since the conventional AMA mentioned previously has the light-reflecting member supported at a single point by means of the post, the light-reflecting member tends to be deformed (twisted or warped) under its own weight. Thus, the AMA encounters difficulty in maintaining good flatness of the reflective surface over a long period of time. By contrast, the piezoelectric/electrostrictive device of the present invention is configured such that the reflective portion extends from an end part of the deformable portion while having a width substantially equal to that of the deformable portion. Thus, the reflective portion is supported over a long distance and can be enhanced in rigidity. Therefore, the reflective portion is unlikely to be deformed and can maintain good flatness of the reflective surface.
The piezoelectric/electrostrictive device of the present invention may be configured such that a plurality of functional elements are arranged linearly adjacent to one another, to thereby enable application to an optical switch, an exposure unit, or a like unit. In this case, the plurality of functional elements preferably have the respective base portions formed into a common base portion.
The piezoelectric/electrostrictive device of the present invention can be configured such that a plurality of functional elements are arranged in a matrix and adjacent to one another, to thereby enable application to an optical switch, an image display unit, an exposure unit, or a like unit. In this case, at least a column of functional elements in the matrix preferably have the respective base portions formed into a common base portion.
Further, the piezoelectric/electrostrictive device of the present invention is preferably configured such that the base portion, the deformable portion, and the reflective portion of the functional element are formed of a unitary body of ceramics.
By virtue of characteristics of ceramics, the deformable portion can be formed thin and readily deformable in the direction of thickness and does not cause permanent elongation within the plane thereof, which would otherwise result from repeated deformation as in the case of a metal film. Also, since the base portion, the deformable portion, and the reflective portion are formed of a unitary body without use of adhesive, the present invention provides a piezoelectric/electrostrictive device of small size having a light modulation mechanism and exhibiting desirable characteristics and excellent durability.
In this case, preferably, the piezoelectric/electrostrictive element is a film-type piezoelectric/electrostrictive element and is integrated with the deformable portion through firing.
Accordingly, the piezoelectric/electrostrictive element of small size can be easily formed, and the operating voltage of the piezoelectric/electrostrictive device can be lowered. Since there is no need to bond the piezoelectric/electrostrictive element to the deformable portion by use of, for example, adhesive, strain that the piezoelectric/electrostrictive element generates can be efficiently utilized without involvement of any loss.
The present invention provides another piezoelectric/electrostrictive device comprising a functional element, which, in turn, comprises a base portion; a deformable portion assuming the form of a thin plate and extending from the base portion to thereby form a plane; a piezoelectric/electrostrictive element tightly fixed to at least the deformable portion; a reflective portion extending from the deformable portion so as to form an active plane intersecting with the plane of the deformable portion, and having a light-reflecting member disposed on the active plane; and a holder portion extending from the base portion in opposition to the deformable portion to thereby hold a part of the reflective portion. Upon operation of the piezoelectric/electrostrictive element, the deformable portion deforms in a direction substantially perpendicular to the plane of the deformable portion to thereby change a reflection angle of light reflected from the reflective portion without deformation of the holder portion.
The present piezoelectric/electrostrictive device is similar to the previously mentioned piezoelectric/electrostrictive device of the present invention, except that a holder portion extends from the base portion in opposition to the deformable portion to thereby hold a part of the reflective portion. The holder portion is formed in such a structure (for example, in a rigid structure) as not to be deformed even when the piezoelectric/electrostrictive element causes the deformable portion to be deformed with a resultant change in a reflection angle of light reflected from the reflective portion.
Accordingly, the present piezoelectric/electrostrictive device not only provides advantages similar to those of the previously mentioned piezoelectric/electrostrictive device of the present invention, but also can prevent deviation of an optical axis from the reflective portion when the reflective portion is driven in order to change the reflection angle of light reflected from the reflective portion, since the holder portion prevents the center of tilting motion of the reflective portion from moving with respect to the base portion.
In this case, the reflective portion preferably extends from an end part of the deformable portion while having a width substantially equal to that of the deformable portion.
Since the reflective portion is supported over a long distance by means of the deformable portion and can be enhanced in rigidity, the reflective portion is unlikely to be deformed and can maintain good flatness of the reflective surface.
The present piezoelectric/electrostrictive device may be configured such that a plurality of functional elements are arranged linearly adjacent to one another, to thereby enable application to an optical switch, an image display unit, an exposure unit, or a like unit. In this case, the plurality of functional elements preferably have the respective base portions formed into a common base portion.
The present piezoelectric/electrostrictive device can be configured such that a plurality of functional elements are arranged in a matrix and adjacent to one another, to thereby enable application to an optical switch, an image display unit, or exposure unit, or a like unit. In this case, at least a column of functional elements in the matrix preferably have the respective base portions formed into a common base portion.
Further, the present piezoelectric/electrostrictive device is preferably configured such that the base portion, the deformable portion, the reflective portion, and the holder portion of the functional element are formed of a unitary body of ceramics.
By virtue of characteristics of ceramics, the deformable portion can be formed thin and readily deformable in the direction of thickness and does not cause permanent elongation within the plane thereof, which would otherwise result from repeated deformation as in the case of a metal film. Also, since the base portion, the deformable portion, the reflective portion, and the holder portion are formed of a unitary body without use of adhesive, the present invention provides a piezoelectric/electrostrictive device of small size having a light modulation mechanism and exhibiting desirable characteristics and excellent durability.
In this case, preferably, the piezoelectric/electrostrictive element is a film-type piezoelectric/electrostrictive element and is integrated with the deformable portion through firing.
Thus, the piezoelectric/electrostrictive element of small size can be easily formed, and the operating voltage of the piezoelectric/electrostrictive device can be lowered. Since there is no need to bond the piezoelectric/electrostrictive element to the deformable portion by use of, for example, adhesive, strain that the piezoelectric/electrostrictive element generates can be efficiently utilized without involvement of any loss.
The present invention further provides a method for fabricating a piezoelectric/electrostrictive device in which a thin (thin wall-like) deformable portion made of ceramics and extending from a thick (thick wall-like) base portion formed of ceramics is deformed by a piezoelectric/electrostrictive element tightly fixed to at least the deformable portion to thereby change angle of a reflective portion made of ceramics and extending from the deformable portion. The method comprises a lamination step of placing a ceramic green sheet on another ceramic green sheet having a substantially rectangular through-hole at a central portion thereof, in such a manner as to cover the through-hole; a firing step of firing the laminated ceramic green sheets to thereby form a unitary body of ceramics having a thick (thick wall-like) portion and a thin (thin wall-like) portion; an element forming step of forming a piezoelectric/electrostrictive element on at least the thin (thin wall-like) portion; a first cutting step of cutting off a part of the thick (thick wall-like) portion from the unitary body so as to leave a residual thick (thick wall-like) portion having a predetermined thickness as measured from an end of the thin (thin wall-like) portion; and a second cutting step of cutting the residual thick portion along a plane perpendicularly intersecting with a cut surface formed as a result of cutting in said first cutting step, to thereby form the reflective portion having the predetermined thickness, the thin (thin wall-like) deformable portion, and the thick (thick wall-like) base portion.
By this method, in particular, the piezoelectric/electrostrictive device having a plurality of functional elements arranged thereon linearly or in a matrix and adjacent to one another can be fabricated efficiently in a reduced number of steps.
In this case, the method of the present invention preferably comprises the additional steps of preparing a plurality of unitary bodies of ceramics having undergone the first cutting step but not having undergone the second cutting step, and bonding the plurality of unitary bodies of ceramics at those parts of the thick (thick wall-like) portions which are to become base portions, while spacers are interposed therebetween; and forming a light-reflecting member on the reflective portions.
Thus, the piezoelectric/electrostrictive device having a plurality of functional elements, each having the reflective portion, arranged linearly or in a matrix and adjacent to one another can be easily fabricated. Also, the device can be fabricated while the distance between the unitary bodies is managed accurately and simply by means of the spacers.
The second cutting step preferably is a step of cutting at least the residual thick (thick wall-like) portion formed as a result of cutting in the first cutting step, the light-reflecting member, and the thin portion.
Thus, the base portion, the deformable portion, and the reflective portion can be simultaneously formed in a single cutting operation in the second cutting step.
Further, the step of forming a piezoelectric/electrostrictive element may be a step of forming a plurality of piezoelectric/electrostrictive elements arranged such that substantially the same clearance is established therebetween; the method of the present invention may comprise an additional step of slitting, before the second cutting step, the thin (thin wall-like) portion between the piezoelectric/electrostrictive elements to thereby form slits in the thin (thin wall-like) portion; and the second cutting step may be a step of cutting at least the residual thick (thick wall-like) portion formed as a result of cutting in the first cutting step, and the light-reflecting member, along planes aligned with the slits. Further, in this case, the slitting step of slitting the thin (thin wall-like) portion preferably is a step of forming the slits in the thin (thin wall-like) portion through laser beam processing; and the second cutting step preferably is a step of cutting, through laser beam processing, the residual thick (thick wall-like) portion and the light-reflecting member.
Since the thin (thin wall-like) portion is slit at positions located along or between the piezoelectric/electrostrictive elements, the second cutting step can be a mere step of cutting at least the residual thick (thick wall-like) portion formed as a result of cutting in the first cutting step, and the light-reflecting member, along planes aligned with the slits. As a result, load (stress) to be imposed on the piezoelectric/electrostrictive device during the second cutting step can be reduced, thereby effectively suppressing occurrence of breakage of a product during fabrication. Through use of laser beam processing for slitting and cutting in the second cutting step, load to be imposed on the device during cutting can be greatly reduced.
In this case, the step of forming the light-reflecting member preferably comprises a step of polishing, before the light-reflecting member is formed, the cut surface formed as a result of cutting in the first cutting step; and the method of the present invention preferably comprises the additional steps of filling a filler into gaps between the plurality of unitary bodies after the plurality of unitary bodies are bonded at the thick (thick wall-like) portions while the spacers are interposed therebetween, and before the polishing step; and removing the filler after the second cutting step.
As mentioned above, after the plurality of unitary bodies are bonded at the thick (thick wall-like) portions while the spacers are interposed therebetween, and before the light-reflecting member is formed, a filler is filled into gaps between the plurality of unitary bodies, followed by polishing the surface on which the light-reflecting member is to be formed. Subsequently, the light-reflecting member is formed on the polished surface. Then, at least the light-reflecting member and the residual thick (thick wall-like) portion are cut. Finally, the filler is removed. Since the filler is present between the plurality of unitary bodies during polishing and cutting in the second cutting step, polishing and cutting can be stably performed.